Multi-beam pattern generator

ABSTRACT

A scanning pattern generator and a method for microlithographic multi-beam writing of high precision patterns on a photosensitive substrate ( 11 ), the system comprising a light source ( 1 ), preferably a laser, for generating at least two light beams, a computer-controlled light modulator ( 4 ), a deflector for scanning the beams on the substrate and an objective lens ( 10 ) to contract the at least one light beam from the light source before it reaches the substrate, wherein at least the objective lens is arranged on a carrier ( 22 ) being movable relative to the substrate ( 11 ) and the light source ( 1 ). Hereby, the carrier defines a movable optical path relative to the remaining, stationary optical path. Further, the system comprises means for altering the stationary optical path in order to maintain telecentricity for the beams as they impinge on the photosensitive substrate during the movement of the carrier and the movable optical path.

This application is the national phase under 35 U.S.C. §371 of PCTInternational Application No. PCT/SE01/01443 which has an Internationalfiling date of Jun. 25, 2001, which designated the United States ofAmerica.

FIELD OF THE INVENTION

The present invention relates to a system and a method formicrolithographic multi-beam writing on photosensitive substrates, andespecially printing of patterns with extremely high precision, such asphotomasks for semiconductor device patterns, display panels, integratedoptical devices and electronic interconnect structures. The termswriting and printing should be understood in a broad sense, meaningexposure of photoresist and photographic emulsion, but also the actionof light on other light sensitive media such as dry-process paper, byablation or chemical processes activated by light or heat. Light is notlimited to mean visible light, but a wide range of wavelengths frominfrared to extreme UV.

BACKGROUND OF THE INVENTION

A system and method for microlithographic writing of a substrate ispreviously known from e.g. EP 0 467 076 by the same applicant. Anexample of a system for microlithographic writing, as is shown in FIG.1, comprises a light source 1, such as a laser, one or more reflectingmirrors 2 to direct the beam in the intended direction, a first lens 3to contract the light beams, a modulator 4 to produce the desiredpattern to be written, and a second lens 5 after the modulator. Themodulator is controlled according to input data. A deflector is used toscan the beams on the substrate 11, and lenses 7, 8, 10 are used tocontract and focus the beams on the substrate. The deflector could be amovable reflective element, such as a mirror. However, severalfunctionally equivalent scanners such as acusto-optic deflectors etc.could also be used. Further, the substrate is preferably arranged on anobject table.

A relative motion between the lens 10 and the table (stage) could beprovided by arranging at least the objective lens 10, and preferably thelenses 7–8 and the deflector 6 as well, on a carrier. Hereby, thecarrier could be moved relative to the substrate, and relative to thelight source in a direction essentially perpendicular to the scanningdirection.

If such a prior art system should be used with several beamsconcurrently being directed to the substrate, so called multi-beamwriting, in order to improve the writing speed, several problems wouldarise.

It is important to obtain a gauss stationary illumination in the lensstop, but this proves difficult to obtain when using multi-beam incombination with a movable carrier. If such illumination is notobtained, beams will impinge on the substrate at different angles,whereby small differences in focus on the substrate, which isinevitable, will result in detrimental variations in the scanninglengths. For several applications, a maximum variation in scanninglength of 20 nm is required. Therefore, a high degree of telecentricity,i.e. the beams being parallel during the scanning, is required. Toobtain this it is important that the beams are superposed on each otherin the deflector, but this proves to be difficult to obtain due to thevarying distance between the deflector on the carrier and the modulator.

Specifically, using multi-beam writing in a pattern generator where partof the optical path is movable will cause problems. FIG. 2 a illustratesa pattern generator where the movable optical path is in an intermediateposition. In this case, the beams will coincide in the deflector 6, anda satisfying telecentricity will be obtained. However, when the carrieris moved to an end position, as is illustrated in FIG. 2 b, the beamswill not coincide in the deflector, but be displaced from each other.Hereby, the beam path in the objective lens 10 will be oblique, and thetelecentricity will be severely deteriorated. There will also be a lossin radiation energy, since part of the beams will be displaced from theworking part of the lenses.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a systemand a method for microlithographic multi-beam writing, whereby therelated problems in the prior art are overcome or at least alleviated.

This object is achieved with a system according to the appended claims.

According to the invention a scanning pattern generator and a method areprovided for microlithographic multi-beam writing of high precisionpatterns on a photosensitive substrate (11). The system comprises alight source (1), preferably a laser, for generating at least two lightbeams, a computer-controlled light modulator (4), a deflector forscanning the beams on the substrate and an objective lens (10) tocontract the at least one light beam from the light source before itreaches the substrate, wherein at least the objective lens is arrangedon a carrier (22) being movable relative to the substrate (11) and thelight source (1), wherein the carrier defines a movable optical pathrelative to the remaining, stationary optical path. Further, itcomprises means for altering the stationary optical path in order tomaintain telecentricity for the beams as they impinge on thephotosensitive substrate during the movement of the carrier and themovable optical path.

Hereby, the stationary optical path could automatically be adjusted inorder to maintain the telecentricity.

Preferably, the deflector (6) is arranged on the carrier, wherein themeans for altering the stationary optical path are arranged to make thebeams coincide in the deflector.

According to a first aspect of the invention, the means for altering thestationary optical path comprises means (24) for altering the spatialpath length of the stationary optical path, such as an optical detour(24) comprising movable reflecting elements.

According to a second aspect of the invention, the means for alteringthe stationary optical path comprises a controllable beam splitter (20).This beam splitter is preferably movable, and preferably comprises adiffractive optical element.

According to a third aspect of the invention, the means for altering thestationary optical path comprises at least one movable lens beingarranged after the modulator.

BRIEF DESCRIPTION OF THE DRAWINGS

For exemplifying purposes, the invention will be described in closerdetail in the following with reference to embodiments thereofillustrated in the attached drawings, wherein:

FIG. 1 is a schematic view of a prior art single-beam system;

FIGS. 2 a and 2 b is a schematic view of a multi-beam system,illustrating the problem with deteriorated telecentricity;

FIG. 3 a is a schematic view of a system according to a first embodimentof the invention;

FIG. 3 b is a schematic view of a system according to a secondembodiment of the invention; and

FIG. 3 c is a schematic view of a system according to a thirdembodiment-of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

The system according to the invention is preferably a laser scannersystem, such as is known from EP 0 467 076, hereby introduced byreference, but with imporved properties for multi-beam writing. Hence,the system is a multi-beam system, where the system preferably comprisesa beam splitter to divide the beam from the light source to severalbeams, exposing the substrate in several scan lines simultaneously.

Referring to FIG. 3 a, the system according to a first, preferredembodiment of the invention comprises a light source 1, preferably alaser, a beam-splitter 20 to divide the beam from the light source intoseveral beams, a computer-controlled light modulator 4 and an objectivelens 10 to contract the light beam from the light source before itreaches the photosensitive substrate 11. Further, the system preferablycomprises one or more reflecting mirrors 2 to direct the beam in theintended direction, a modulator 4 to produce the desired pattern to bewritten, a first lens 3 to contract the light beams on the modulator,and a second (collimator) lens 5 after the modulator to direct the beamstowards a deflector 6. The modulator is controlled according to inputdata.

The deflector 6 is used to scan the beams on the substrate 11, andlenses 7, 8, 10 are used to contract and focus the beams on thesubstrate. Further, a lens stop 9 is preferably used to preventstray-light from impinging on the substrate. The deflector could be amovable reflective element, such as a mirror. However, severalfunctionally equivalent scanners such as acusto-optic deflectors etc.could also be used. Further, the substrate 11 is preferably arranged onan object table.

At least the objective lens 10 is placed on a movable carrier 22, butpreferably the deflector 6, and the lenses 7–8 as well are arranged onthe carrier as well. The carrier 22 is movable relative to the substrateand further, movable in the beam direction relative to the modulator andthe other optical elements of the system. The system according to theinvention is specifically useful for writing of large-area substrates,and for such applications the carrier could typically be moved 1100 mmduring operation.

Due to the movement of the carrier, the beams travels at first through astationary optical path, and thereafter on a movable optical path on thecarrier, and is then directed to the substrate.

According to the invention, the system further comprises means foraltering how the beams from the stationary optical path is directed tothe movable optical path. This, means preferably comprises a movablediffractive optical element (DOE) or a controllable beam splitter, andmost preferably a diffractive optical beam splitter 20, arranged aheadof the modulator 4. This optical element 20 is movable, whereby thedirection of the beams being directed to the movable optical path andthe deflector could be altered. Hereby, very limited movements of theoptical element are required in order to achieve sufficienttelecentricity, whereby only a low degree of mechanical precision isneeded. For example, to compensate for movements of about 1100 mm of thecarrier a movement of about +/−35 mm for the optical element isrequired. Hereby, by adjusting the position of the beam splitter or thediffractive optical element it is possible to make the beams coincide inthe deflector, and thereby see to that a satisfactory telecentricity isobtained. This is illustrated in FIG. 3 a, where the position of thecarrier is the same as in FIG. 2 b, but where the beam splitter 20 hasbeen moved to compensate this.

The control of the movement of the optical element is preferablycontrolled synchronized and in relation to the movement of the carrier22. To this end, a controller is preferably provided. Said controller issupplied with a position signal indicating the position of the carrier,and accordingly generates a control signal to the optical element.

In FIG. 3 b, an alternative second embodiment of the invention accordingto the invention is shown. In this embodiment the same referencenumerals are used to indicate similar components. The system accordingto the second embodiment corresponds to the first embodiment describedhereinbefore, but with the difference that the means for altering howthe beams from the stationary optical path is directed to the movableoptical path, and to the deflector, is here one or several movablelenses arranged after the modulator. These movable lenses are preferablythe collimator lenses 5 and 21. Further, movable or stationary lenses,such as lens 25, may be arranged as well. Hence, in this embodiment,one, two or even more movable collimator lenses are used to control thebeams to make them coincide in the deflector and to improve thetelecentricity.

In FIG. 3 c, an alternative third embodiment of the invention accordingto the invention is shown. In this embodiment the same referencenumerals are used to indicate similar components. The system accordingto the second embodiment corresponds to the first embodiment describedhereinbefore, but with the difference that the means for altering howthe beams from the stationary optical path is directed to the movableoptical path, and to the deflector, is here means 24 for altering theoptical path length between the modulator and the deflector. Such meanscould e.g. comprise an optical detour with reflecting elements such asmirrors or prisms, where at least one of the reflecting elements aremovable to increase or decrease the spatial path length, as isillustrated in FIG. 3 c.

Hence, in this third embodiment, the optical path length is altered tocontrol the beams to make them coincide in the deflector and to improvethe telecentricity.

The system according to the invention provides enhanced precision andtelecentricity in an easy way and by means of few components. Hence, thesystem and method according to the invention efficiently compensates forbeam position variations due to deteriorated telecentricity. Thus, theinvention makes microlithographic writing of high precision patternsmore efficient and cost effective, at the same time as the patternprecision is improved.

However several variations of the above-mentioned embodiments arepossible, and obvious for a person skilled in the art. For example,several different means for altering the optical path length arepossible to use, such as optical detours, different controllable beamsplitters, different optical elements and the like. Such obviousmodifications must be considered as being part of the invention, as itis defined by the following claims.

1. A scanning pattern generator comprising: a light source forgenerating at least two light beams; a computer-controlled lightmodulator; a deflector for scanning the beams on a photosensitivesubstrate; an objective lens to contract the at least one light beamfrom the light source before the at least one light beam reaches thephotosensitive substrate; and means for altering the stationary opticalpath in order to maintain telecentricity for the beams as they impingeon the photosensitive substrate during the movement of the carrier and amovable optical path; wherein at least the objective lens is arranged ona carrier, being movable relative to the substrate and the light source,wherein the carrier defines the movable optical path relative to theremaining stationary optical path.
 2. The system according to claim 1,wherein the means for altering the stationary optical path isautomatically controlled in relation to the movement of the carrier. 3.The system according to claim 2, further including a controller suppliedwith a position signal indicating the position of the carrier andgenerating a control signal to control the means for altering thestationary optical path.
 4. The system according to claim 1, wherein thedeflector is arranged on the carrier, and the means for altering thestationary optical path are arranged to make the beams coincide in thedeflector.
 5. The system according to claim 1, wherein the means foraltering the stationary optical path comprises means for altering aspatial path length of the stationary optical path.
 6. The systemaccording to claim 5, wherein the means for altering the stationaryoptical path comprises an optical detour comprising movable reflectingelements.
 7. The system according to claim 1, wherein the means foraltering the stationary optical path comprises a controllable beamsputter.
 8. The system according to claim 7, wherein the beam sputter isa diffractive optical element.
 9. The system according to claim 1,wherein the means for altering the stationary optical path comprises atleast one movable lens being arranged after the modulator.
 10. Thesystem according to claim 1, wherein the modulator is an acousto-opticmodulator.
 11. The system according to claim 1, wherein the deflector isan acousto-optic deflector.
 12. The scanning pattern generator of claim1, wherein the light source is a laser.
 13. A method for scanningmicrolithographic multibeam writing of high precision patterns on aphotosensitive substrate with at least two light beams emitted from alight source and controlled by a computer-controlled light modulator, adeflector for scanning the beams on the substrate and an objective lensto contract the at least one light beam from the light source before itreaches the substrate, wherein at least the objective lens is arrangedon a carrier being movable relative to the substrate and the lightsource, wherein the carrier defines a movable optical path relative to aremaining stationary optical path, the method comprising: altering thestationary optical path in order to maintain telecentricity for thebeams as they impinge on the photosensitive substrate during themovement of the carrier and the movable optical path.
 14. The methodaccording to claim 13, wherein the altering of the stationary opticalpath is automatically controlled in relation to the movement of thecarrier.
 15. The method according to claim 13, wherein the deflector isarranged on the carrier, and the altering of the stationary optical pathmakes the beams coincide in the deflector.
 16. The method according toclaim 13, wherein the altering of a stationary optical path comprisesaltering the spatial path length of the stationary optical path.
 17. Themethod according to claim 13, wherein altering of the stationary opticalpath comprises controlled movement of a movable beam splitter.
 18. Themethod according to claim 13, wherein altering of the stationary opticalpath includes controlled movement of at least one lens being arrangedafter the modulator.
 19. A scanning pattern generator comprising: alight source adapted to generate at least two light beams; acomputer-controlled light modulator; a deflector adapted to scan thebeams on the substrate; an objective lens to contract at least one lightbeam from the light source before the at least one light beam reachesthe substrate; and optics adapted to alter a stationary optical pathsuch that the beams are telecentric as they impinge on the substrateduring the movement of the carrier and a movable optical path; whereinat least the objective lens is arranged on a carrier, movable relativeto the substrate and the light source, and the carrier defines themovable optical path relative to the stationary optical path.
 20. Thescanning pattern generator of claim 19, wherein the optics include atleast one of a movable diffractive optical element and a controllablebeam splitter.
 21. The scanning pattern generator of claim 19, whereinthe optics include at least one collimator lens.
 22. The scanningpattern generator of claim 19, wherein the optics include at least onereflecting element.
 23. The scanning pattern generator of claim 19,wherein the optics include at least one of a mirror and a prism.
 24. Thescanning pattern generator of claim 19, wherein the light source is alaser.
 25. A method for scanning microlithographic multibeam writing ofhigh precision patterns on a substrate, the method comprising: emittingat least two light beams from a light source and controlling the atleast two light beams via a computer-controlled light modulator;contracting at least one light beam before it reaches the substrate;scanning the at least two light beams on the substrate; moving a movableoptical path of the at least two light beams relative to a remainingstationary optical path; and altering the stationary optical path suchthat the at least two beams are telecentric as they impinge on thesubstrate during the movement of a carrier and the movable optical path.